Amplitude shading techniques for sonar, radio and radar arrays have been under development and in use for decades. This invention applies generally but is particularly relevant to sonar transducers wherein series-parallel elements can provide monotonic symmetric discrete shading.
For purposes of illustration, it will be assumed that the elements, generally transducers, are identical and have identical radiation-impedance loading. Then, four elements in series that are in parallel with three elements in series will each have 1/4 and 1/3 amplitude levels respectively. Thus, those seven elements chosen from the discrete sum total of the array have certain discrete amplitudes. It is a special characteristic in these arrays that the discrete amplitudes achieved are related directly to the number and size of elements in the discrete array. Some prior art methods took into consideration optimal choices that are not possible in the discrete amplitude-discrete location array of this invention.
Other prior art methods used discrete amplitude shading for lobe suppression in discrete arrays, but new concepts are required in order to achieve lower side-lobe levels and/or narrower beamwidth combinations.